Organic electroluminescent display device and manufacturing method thereof

ABSTRACT

An electroluminescent display device includes a display panel having scan lines, data lines, and pixel circuits. The pixel circuit includes an electroluminescent element having a first electrode layer, a first insulation film, and an emitting layer for displaying images. A driving circuit is coupled to the electroluminescent element. The first electrode layer is superimposed on a power source line, a scan line, or both, with a second insulation film therebetween.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/984,097, filed Nov. 9, 2004, now U.S. Pat. No. 7,956,533, whichclaims priority to and the benefit of Korean Patent Application No.10-2003-0083589 filed on Nov. 24, 2003 and Korean Patent Application No.10-2004-0000594 filed on Jan. 6, 2004, the entire content of all ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a display device. More specifically,the present invention relates to an organic electroluminescent (EL)display device with an improved aperture ratio.

(b) Description of the Related Art

The organic EL display device, which is a display device forelectrically exciting a fluorescent organic compound to emit light, hasorganic light-emitting cells that are voltage- or current-driven todisplay an image. These organic, light-emitting cells have a structurecomposed of an anode layer, an organic thin film, and a cathode layer.To balance the electrons and holes in order to enhance luminescentefficiency, the organic thin film has a multi-layer structure thatincludes an emitting layer (EML), an electron transport layer (ETL), anda hole transport layer (HTL). The multi-layer structure of the organicthin film can also include an electron injecting layer (EIL) and a holeinjecting layer (HIL).

As shown in FIG. 1, an organic EL display device includes an organic ELdisplay panel (referred to as “display panel” hereinafter) 100, a datadriver 200, and a scan driver 300.

The display panel 100 includes a plurality of data lines D1 to Dmarranged in the column direction, a plurality of scan lines S1 to Snarranged in the row direction, and a plurality of pixel circuits.

Each of the pixel circuits includes a driving transistor 20 forcontrolling the current flowing to an organic EL element 40, a switchingtransistor 10 for applying a voltage at the data line D1 to a gate ofthe driving transistor 20 in response to a select signal provided by thescan line S1, and a capacitor 30 coupled between the gate and the sourceof the driving transistor. The drain of the driving transistor 20 iscoupled to a power source line 50 for transmitting a power sourcevoltage V_(DD).

The data driver 200 supplies data voltages to the data lines D1 to Dm,and the scan driver 300 sequentially applies select signals forselecting pixel circuits to the scan lines S1 to Sn.

FIG. 2 shows a plan view of a pixel circuit coupled to the scan line S1and the data line D1 in the organic EL display device shown in FIG. 1,and FIG. 3 shows a cross-sectional view of the part of A-A′ of FIG. 2.

As shown in FIGS. 2 and 3, a gate electrode 16 of the switchingtransistor 10 is formed on the same electrode layer as that of the scanline S1, and a source region 13 of the switching transistor 10 iscoupled to the data line D1 by a contact hole. Drain region 14 of theswitching transistor 10 is coupled to a gate electrode of the drivingtransistor 20 through a contact hole. The drain region of the drivingtransistor 20 is coupled to the power source line 50 through a contacthole, and a source region is coupled to the pixel electrode layer 42 ofthe organic EL element 40 by a contact.

Transparent insulation film 12 is formed on a substrate film 11. A firstinsulation film 15 is formed on the polycrystalline silicon layer, and agate electrode 16 is formed to cross the polycrystalline silicon layeron the first to insulation film 15.

Part of the polycrystalline silicon layer beneath the gate electrode 16is not doped, and two parts thereof are doped with n-type dopant. Theregions doped with the dopant form a source region 13 and a drain region14 respectively, and the undoped region forms a channel region.

A source electrode 18 is formed on the source region 13, and the sourceregion 13 is coupled to the data line D1 through the source electrode18. A drain electrode 19 is formed on a drain region 14, and the drainelectrode 19 is coupled to a gate electrode of the second transistor 20.

The organic EL element 40 comprises an organic EML 41 and a pixelelectrode layer 42, such as indium tin oxide (ITO). The organic ELelement 40 is positionally separated from the power source line 50. Acathode electrode 21 is formed on the organic EML 41.

The organic EML 41 is formed at a pixel region defined by an insulationfilm which forms an aperture on the pixel electrode layer 42. That is,since the organic EML 41 is formed within the pixel electrode layer 42,the region for forming the organic EML 41 is limited by the pixelelectrode layer 42. Therefore, the narrow region of the generatedorganic EML 41 degrades the aperture ratio of the pixel circuit. It istherefore desirable to improve the aperture ratio of an organic ELdisplay device.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, an electroluminescent (EL)display device includes a display panel including a plurality of scanlines, a plurality of data lines, and a plurality of pixel circuits. Thepixel circuit includes an EL element with a first electrode layer, afirst insulation film, and an emitting layer (EML). The circuit furtherincludes a driving circuit coupled to the EL element. The firstelectrode layer of the EL element is superimposed on a power sourceline, with a second insulation film therebetween. Within the context ofthis disclosure, “superimposed” indicates that the element is covering,overlapping, or aligned in a vertical direction with another element,with or without intervening elements therebetween.

In an alternate embodiment, the first electrode layer of the EL elementis superimposed on the scan line with the second insulation filmtherebetween.

In another embodiment, a method is provided for manufacturing an ELdisplay device that includes an EL element, a first insulation film, anda driving circuit, as described above. The method includes forming apower source line for supplying power to the driving circuit, coveringthe power source line with a second insulation film, forming a firstelectrode layer of the EL element on the second insulation film, andsuperimposing part of the first electrode layer on the power sourceline. The embodiment further includes forming a third insulation filmwith an aperture on a part of the first electrode layer that is spacedhorizontally from the power source line, forming an emitting layer ofthe EL element on the aperture, and forming a second electrode layer onthe emitting layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conventional voltage programming organic EL displaydevice.

FIG. 2 shows a plan view of a pixel circuit of the organic EL displaydevice shown in FIG. 1.

FIG. 3 shows a cross-sectional view of the part of A-A′ of the pixelcircuit of FIG. 2.

FIG. 4 shows a simplified plan view of a pixel circuit according to anexemplary embodiment of the present invention.

FIG. 5 shows a detailed plan view of a pixel circuit according toanother exemplary embodiment of the present invention.

FIG. 6 shows a cross-sectional view of the part of B-B′ of the pixelcircuit of FIG. 5.

FIG. 7 shows an alternate embodiment of the cross-sectional view of thepart of B-B′ of the pixel circuit of FIG. 5 with a wider organic EML.

FIG. 8 shows an application of a pixel circuit according to an exemplaryembodiment of the present invention to a front-type light emittingdisplay device.

FIG. 9 shows a pixel circuit according to another exemplary embodimentof the present invention.

DETAILED DESCRIPTION

Throughout this description, thicknesses are magnified in the drawingsto clearly depict the plurality of layers and regions. Similar parts orunits have the same reference numerals throughout the specification. Inthe context of this disclosure, when a layer, a film, a region, or asubstrate is described as being “on” another part, “on” should beunderstood to include either direct contact or coupling through at leastone intervening material.

The exemplary embodiments described are applied to a rear-type lightemitting display device. However, it is within the scope of theinvention to apply the embodiments to front-type light emitting displaydevices as well.

FIG. 4 shows a simplified plan view of a pixel circuit according to anexemplary embodiment of the present invention. For ease of description,a single pixel circuit driven by a scan line S1, a data line D1, and apower source line 250 is described.

As shown in FIG. 4, the pixel circuit comprises an organic EL element240 for displaying images in correspondence to an amount of the appliedcurrent, and a driving circuit 280 for driving the organic EL element240.

The organic EL element 240 comprises an organic EML, a first electrodelayer for forming an anode (ITO), and a second electrode layer (notillustrated) for forming a cathode.

The driving circuit 280 can be formed by using a voltage programming orcurrent programming driving circuit, and it controls the current flowingto the organic EL element 240 according to images signals applied to thedata line to thereby represent desired images when a select signal isapplied from the scan line.

The first electrode layer forming the anode is formed to be superimposedon the power source line 250. Since a constant power source voltage isapplied to the power source line 250, a minor variation of data appliedto the first electrode layer substantially causes no influence to thepower source line 250.

Therefore, when the first electrode layer is formed to be superimposedon the power source line 250, the organic EML is formed more widely, andthe aperture ratio of the organic EL display device is improved.

FIG. 5 shows a detailed plan view of a pixel circuit according to anexemplary embodiment of the present invention, and FIG. 6 shows across-sectional view of the part of B-B′ of the pixel circuit of FIG. 5.

As shown in FIGS. 5 and 6, a driving circuit 180 comprises a drivingtransistor 120 for controlling the current flowing to the organic ELelement 140 according to the voltage applied to a gate, a switchingtransistor 110 for transmitting image signals applied to the data lineD1 to the driving transistor 120 in response to a select signal, and acapacitor 130.

The gate electrode 116 of the switching transistor 110 is formed on thesame electrode layer as that of the scan line S1, and a source region113 of the switching transistor 110 is coupled to the data line D1through a contact hole. A drain region 114 of the switching transistor110 is coupled to a gate electrode 116 of the driving transistor 120through a contact hole.

Drain region of the driving transistor 120 is coupled to the powersource line 150 by a contact hole, and a source region of the drivingtransistor 120 is coupled to the electrode layer 142 of the organic ELelement 140 by a contact hole.

In this embodiment, an insulation film is formed between the electrodelayer 142 of the organic EL element 140 and the power source line 150,and part of the electrode layer 142 is formed to be superimposed on thepower source line 150 with the insulation film therebetween.

The capacitor 130 is formed by the power source line 150 and the gateelectrode of the driving transistor 120.

As a result, when the switching transistor 110 is turned on by theselect signal, the data voltage is transmitted to the gate of thedriving transistor 120, and a predetermined current is applied to theelectrode layer 142. Holes injected from the electrode layer 142 aretransferred to the EML via the HTL of the organic EML 141, and electronsare injected to the EML via the ETL of the organic EML 141 from acathode electrode layer (not illustrated). The electrons and the holesare recombined in the EML to generate excitrons, and phosphorousmolecules of the EML emit light as the excitrons are modified to theground state from the excitation state. In this instance, the emittedlight is output through the transparent electrode layer 142, theinsulation film, and the substrate to thus form images.

As shown, the organic EL display device is a rear-type light emittingdisplay device in which a polycrystalline silicon layer is formed on atransparent insulation film 112. The transparent insulation film 112 isformed on a substrate film 111. A first insulation film 115 made of SiO2or SiNx is formed on the polycrystalline silicon layer.

A gate electrode 116 made of Al and Cr is formed to cross thepolycrystalline silicon layer on the first insulation film 115.

Part of the polycrystalline silicon layer beneath the gate electrode 116is not doped, and two parts thereof are doped with n-type dopant. Theregions doped with the dopant form a source region 113 and a drainregion 114 respectively, and the undoped region forms a channel region.

A source electrode 118 is formed on the source region 113, and thesource region 113 is coupled to the data line D1 through the sourceelectrode 118. A drain electrode 119 is formed on a drain region 114,and the drain electrode 119 is coupled to a gate electrode of the secondtransistor 120.

The power source line 150 is formed on the first insulation film 115,and is covered by a second insulation film 117. The electrode layer 142of the organic EL element 140 is formed on the second insulation film117 between the transistor 110 and the power source line 150. Theelectrode layer 142 is extended to the top of the power source line 150,and a third insulation film 125 with an aperture is formed on theelectrode layer 142. In this instance, the third insulation film 125 isformed to cover part of an edge of the electrode layer 142.

In the case that the organic EL display device is a rear-type lightemitting display device, the aperture of the third insulation film 125is formed on a part where the electrode layer 142 is not superimposed onthe power source line 150, and an organic EML 141 is formed on theaperture of the third insulation film 125. A deposited cathode electrode121 is formed on the organic EML 141, and the cathode electrode 121 isformed as a metallic layer.

FIG. 7 shows a cross-sectional view of the part of B-B′ of the pixelcircuit in an alternate embodiment showing the organic EML 141′ formedthe most widely.

As shown, the organic EML 141′ is formed nearest the power source line150 within a range that the organic EML 141′ is not bent.

When the thickness of the second insulation film 117 is defined as ‘ID’and the thickness of the electrode layer 142 is defined as ‘a,’ theaperture of the third insulation film 125 is separately formed from thepower source line 150 by a distance equal to the summation of thethickness ‘a’ and ‘b.’ The aperture ratio of the organic EL displaydevice can thereby become maximized.

The aperture ratio is increased because the organic EML 141′ is formedmore widely by superimposing the electrode layer 142 on the power sourceline 150 with the second insulation film 117 therebetween.

FIG. 8 applies an alternate embodiment of the pixel circuit to afront-type light emitting display device.

As shown, the case of applying the concept of the present invention tothe front-type light emitting display device is different from therear-type light emitting display device shown in FIG. 6 in that asubstantially flattened film 122 is formed on the second insulation film117.

The flattened film 122 is formed with an organic film. Also, theelectrode layer 142′ is formed with a metallic layer for reflectinglight, and the electrode layer 121′ is formed with a transparentelectrode layer. The electrode layer 142′ is formed to be superimposedon the power source line 150 with the second insulation film 117therebetween.

FIG. 9 shows a pixel circuit according to another exemplary embodimentof the present invention.

As shown, the pixel circuit is different from the pixel circuit of FIG.5 in that the electrode layer 142″ is superimposed on the power sourceline 150 and the scan line S2.

Since a constant voltage signal is applied to the scan line S2 during aselect time of the pixel circuit, minor voltage variation caused by theelectrode layer 142″ substantially generates no influence to the selectsignal applied to the scan line S2.

The light emitting region is maximized and the aperture ratio of theorganic EL display device is increased by superimposing the electrodelayer 142″ on the scan line S2 to which the constant voltage is applied.

The third insulation film with the aperture is formed on the electrodelayer 142″, and the organic EML 141 is formed on the aperture. In thisembodiment, the aperture of the third insulation film is horizontallyseparated from the power source line 150 at least by a distance equal tothe summation of the thickness of the second insulation film and theelectrode layer 142″.

FIG. 9 shows that the electrode layer 142″ is superimposed on thenext-row scan line S2. However, it is also within the scope of theinvention for the electrode layer 142 to be superimposed on the currentscan line 51. The electrode layer 142 can alternatively be superimposedon the next-row scan line S2 without being superimposed on the powersource line 150.

Although exemplary embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive concepttaught herein, which may appear to those skilled in the art, will stillfall within the spirit and scope of the present invention, as defined inthe appended claims.

Specifically, the above-described driving circuit has been described interms of a voltage programming circuit including a driving transistorand a switching transistor. Without being restricted to this circuittype, the driving circuit can be formed with the current programmingmethod as well as various voltage programming methods.

The power source line 150 has been described to be a separately formedelement, but it can alternatively be formed as a gate electrode of atransistor or a source/drain electrode. In these alternate embodiments,the electrode layer of the organic EL element is superimposed on thegate electrode or the source/drain electrode with an insulation filmtherebetween.

The above-described driving transistor and the switching transistor havebeen described to have N channel transistors, but one skilled in the artwill realize that the switching transistor may be formed in any suitablemanner including a first electrode, a second electrode, and a thirdelectrode, with the voltage applied to the first electrode and thesecond electrode controlling the current flowing to the third electrodefrom the second electrode.

1. A method for manufacturing an electroluminescent display deviceincluding an electroluminescent element, a first insulation film, and adriving circuit coupled to the electroluminescent element, comprising:(a) forming a power source line for supplying power to the drivingcircuit; (b) forming the first insulation film to cover the power sourceline; (c) forming a first electrode layer of the electroluminescentelement on the first insulation film, and superimposing at least part ofthe first electrode layer on the power source line; (d) forming a secondinsulation film having an aperture on a part of the first electrodelayer that is horizontally separated from the power source line; (e)forming an emitting layer of the electroluminescent element on theaperture; and (f) forming a second electrode layer on the emittinglayer, wherein the forming of the emitting layer comprises horizontallyseparating the emitting layer of the electroluminescent element from thepower source line by a distance equal to or greater than a summation ofthicknesses of the first insulation film and the first electrode layer.2. The method of claim 1, wherein the first electrode layer is formed bya transparent electrode layer or a metallic layer.
 3. The method ofclaim 2, wherein the second electrode layer is formed by a metalliclayer or a transparent electrode layer.
 4. The method of claim 1,wherein the second insulation film is an insulation film for defining apixel region.
 5. The method of claim 1, further comprising forming asubstantially flattened layer that comprises an organic film on thefirst insulation film, before forming the first electrode layer.
 6. Amethod for manufacturing a bottom emission type electroluminescentdisplay device comprising a display panel including a plurality of scanlines, a plurality of data lines, and a plurality of pixel circuits on asubstrate, each of the pixel circuits including an electroluminescentelement, a first insulation film, and a driving circuit coupled to theelectroluminescent element, the method comprising: (a) forming the scanlines on the substrate; (b) forming the first insulation film to coverthe scan lines; (c) forming a transparent electrode layer of theelectroluminescent element on the first insulation film and at leastpartially overlapping one of the scan lines; and (d) forming an emittinglayer of the electroluminescent element on the transparent electrodelayer.
 7. The method of claim 6, further comprising forming a secondinsulation film on the first insulation film and having an aperture on apart of the transparent electrode layer that is horizontally separatedfrom the one of the scan lines, wherein the forming of the emittinglayer further comprises forming the emitting layer on the aperture, andwherein the second insulation film is an insulation film for defining apixel region.
 8. The method of claim 6, further comprising forming apower source line on the substrate, the power source line being forsupplying power to the driving circuit, wherein the forming of the firstinsulation film further comprises forming the first insulation film tocover the power source line, and wherein the forming of the transparentelectrode layer further comprises forming the transparent electrodelayer to at least partially overlap the power source line.
 9. The methodof claim 8, further comprising forming a second insulation film on thefirst insulation film and having an aperture on a part of thetransparent electrode layer that is horizontally separated from thepower source line, wherein the forming of the emitting layer furthercomprises forming the emitting layer on the aperture.
 10. The method ofclaim 6, further comprising forming a reflective electrode comprising ametallic layer on the emitting layer, wherein the reflective electrodeis configured to reflect light from the emitting layer toward thesubstrate and through the transparent electrode for bottom emission. 11.The method of claim 6, further comprising forming a second insulationfilm on the first insulation film and having an aperture on a part ofthe transparent electrode layer that is horizontally separated from theone of the scan lines, wherein the aperture is horizontally separatedfrom the one of the scan lines by a distance equal to or greater than asummation of thicknesses of the first insulation film and thetransparent electrode layer.
 12. The method of claim 6, furthercomprising forming a second insulation film on the first insulation filmand having an aperture on a part of the transparent electrode layer thatis horizontally separated from the one of the scan lines, wherein theforming of the emitting layer further comprises forming the emittinglayer on the aperture.
 13. The method of claim 12, wherein the formingof the emitting layer further comprises horizontally separating theemitting layer from the one of the scan lines by a distance equal to orgreater than a summation of thicknesses of the first insulation film andthe transparent electrode layer.
 14. The method of claim 6, wherein theforming of the emitting layer further comprises horizontally separatingthe emitting layer from the one of the scan lines by a distance equal toor greater than a summation of thicknesses of the first insulation filmand the transparent electrode layer.